Ubuntu Manpage: v.surf.idw - Provides surface interpolation from vector point data by Inverse Distance Squared

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Provided by: grass-doc_7.0.3-1build1_all

NAME

       v.surf.idw   -  Provides  surface  interpolation  from  vector  point  data  by  Inverse Distance Squared
       Weighting.

KEYWORDS

       vector, surface, interpolation, IDW

SYNOPSIS

       v.surf.idw
       v.surf.idw --help
       v.surf.idw [-n] input=name  [layer=string]   [column=name]  output=name  [npoints=count]    [power=float]
       [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       -n
           Don’t index points by raster cell
           Slower but uses less memory and includes points from outside region in the interpolation

       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       input=name [required]
           Name of input vector map
           Or data source for direct OGR access

       layer=string
           Layer number or name
           Vector  features  can have category values in different layers. This number determines which layer to
           use. When used with direct OGR access this is the layer name.
           Default: 1

       column=name
           Name of attribute column with values to interpolate
           If not given and input is 2D vector map then category values are used. If input is 3D vector map then
           z-coordinates are used.

       output=name [required]
           Name for output raster map

       npoints=count
           Number of interpolation points
           Default: 12

       power=float
           Power parameter
           Greater values assign greater influence to closer points
           Default: 2.0

DESCRIPTION

       v.surf.idw  fills  a  raster  matrix  with interpolated values generated from a set of irregularly spaced
       vector data points using numerical approximation (weighted averaging) techniques. The interpolated  value
       of  a  cell  is  determined by values of nearby data points and the distance of the cell from those input
       points.  In comparison with other methods, numerical approximation allows representation of more  complex
       surfaces (particularly those with anomalous features), restricts the spatial influence of any errors, and
       generates the interpolated surface from the data points.

       Values to interpolate are read from column option. If this option is not  given  than  the  program  uses
       categories as values to interpolate or z-coordinates if the input vector map is 3D.

NOTES

The amount of memory used by this program is related to the number of vector points in the current
region. If the vector point map is very dense (i.e., contains many data points), the program may not be
able to get all the memory it needs from the system. The time required to execute is related to the
resolution of the current region, after an initial delay determined by the time taken to read the input
vector points map.

Note that vector features without category in given layer are skipped.

If the user has a mask set, then interpolation is only done for those cells that fall within the mask.
However, all vector points in the current region are used even if they fall outside the mask. Vector
points outside the current region are not used in the interpolation. A larger region may be set and a
mask used to limit interpolation to a smaller area if it is desired to use vector points from outside the
region in the interpolation. The -n flag may also be used to achieve a similar result.

If more than npoints fall into one target raster cell, the mean of all the site values will determine the
cell value (unless the -n flag is specified, in which case only the npoints closest to the centre of the
cell will be interpolated).

The power parameter defines an exponential distance weight. Greater values assign greater influence to
values closer to the point to be interpolated. The interpolation function peaks sharply over the given
data points for 0 < p < 1 and more smoothly for larger values. The default value for the power parameter
is 2.

By setting npoints=1, the module can be used to calculate raster Voronoi diagrams (Thiessen polygons).

AUTHORS

       Michael Shapiro, U.S. Army Construction Engineering Research Laboratory
       Improved algorithm (indexes points according to cell and ignores points outside current region)  by  Paul
       Kelly

       Last changed: $Date: 2014-12-27 23:51:00 +0100 (Sat, 27 Dec 2014) $

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